1. Field of the Invention
This invention relates to a method for the production of a methylolaminotriazine condensate, the reaction product of cyclohexanecarboguanamine with formaldehyde. More particularly, it relates to a method for highly efficient production of methylolaminotriazine condensate capable of being thoroughly dissolved in such solvents as water, methanol, butanol, and mixtures thereof and consequently giving rise to a homogeneous solution even when the ratio of the amount of formaldehyde to be used to the amount of cyclohexanecarboguanamine is small.
2. Description of the Prior Art
The methylolaminotriazine condensate produced by the reaction of cyclohexanecarboguanamine with formaldehyde has been known to the art. This methylolaminotriazine condensate as used in a shaped article, for example, excels the condensate using melamine in crack resistance and excels the condensate using benzoguanamine in lightfastness and promises a great expansion of the range of uses found therefor.
A method for the production of methylolaminotriazine condensate (hereinafter refeferred to as "CHG resin") by the reaction of cyclohexanecarboguanamine with formaldehyde is described in Japanese Patent Publication SHO 48(1973)-17,756. Specifically, the technique of causing cyclohexanecarboguanamine to react with formaldehyde in an aqueous solution at a temperature in the range of 40.degree. to 80.degree. C. is disclosed in this patent publication. This method is very effective when formaldehyde is used in a large amount. This method, however, has betrayed a disadvantage that when the amount of formaldehyde to be used is decreased to less than 3 mols, particularly to less than 2.5 mols, per mol of cyclohexanecarboguanamine the reaction mixture consequently obtained is turbid and does not form a homogeneous solution.
This phenomenon is peculiar to the CHG resin and is not observed in melamine-, benzoguanamine-, or norbornanecarboguanamine. U.S. Pat. No. 3,379,661 discloses a method for the production of a copolycondensate resin of cyclohexanecarboguanamine and melamine. This copolycondensate resin produces a homogeneous resin solution even when the amount of formaldehyde to be used is less than 3 mols per mol of the total of cyclohexanecarboguanamine and melamine.
A method for the production of the CHG resin by the reaction of cyclohexanecarboguanamine with formaldehyde and an alcohol is described in U.S. Pat. No. 2,859,188. Specifically, the technique of causing 1 mol of cyclohexanecarboguanamine to react with 3 to 6 mols of formaldehyde in a mixed solvent of alcohol and water, with the solution kept refluxed, is disclosed. This method also has a disadvantage that when formaldehyde is used in an amount of less than 3 mols per mol of cyclohexanecarboguanamine, the solution consequently obtained is turbid and cannot be used as a raw material for coating material.
For the conventional techniques to produce a homogeneous CHG resin, it is essential that formaldehyde should be used in an amount of not less than 3 mols per mol of cyclohexanecarboguanamine. In the light of the toxicity of formaldehyde, the use of formaldehyde in such a large amount is sometimes undesirable depending on the use of CHG resin thus obtained. In this respect, the conventional techniques have room for further improvement.
An object of this invention, therefore, is to provide a method for producing a clear and homogeneous CHG resin even when formaldehyde is used in an amount of less than 3 mols per mol of cyclohexanecarboguanamine.